Glucose Transporter 1 (GLUT1) Positivity in Ganglion Cysts: A Diagnostic Caveat Due to Overlap With Perineuriomas and Other Fibromyxoid Lesions.

Glucose transporter 1 (GLUT1) is a sensitive immunohistochemical marker for perineural cells and certain mesenchymal neoplasms, including chordoma, desmoplastic small round cell tumor, desmoid-type fibromatosis, epithelioid sarcoma, gastrointestinal stromal tumor, myoepithelioma, schwannoma, and undifferentiated pleomorphic sarcoma. In this study, we focus on the morphological and immunohistochemical challenges in differentiating between ganglion cysts and perineuriomas. To our knowledge, no previous studies have explored the potential morphological and immunohistochemical similarities between these two lesions. We retrospectively retrieved cases coded as "ganglion cysts" from our departmental archives. Clinical data included the patient's age, gender, lesion location, and size. All slides were reviewed by two pathologists, and 4-μm-thick formalin-fixed paraffin-embedded tissue sections were subjected to immunostaining for epithelial membrane antigen (EMA) and GLUT1. The study included core biopsies and excision specimens from 14 patients (11 females and three males; M:F ratio: 3.6:1), ranging in age from 20 to 89 years (median: 60 years; mean: 53 years). Lesion locations included the finger (six cases), dorsal wrist (five cases), and the knee, volar wrist, and an unspecified hand site (one case each). Morphologically, 11 ganglion cysts were predominantly cystic, with walls composed of dense fibroconnective tissue and focal myxoid changes. These myxoid areas contained spindled and stellate cells within a myxoid stroma. The remaining three cases exhibited a predominantly solid morphology, characterized by dense fibroblastic-myofibroblastic stroma with limited myxoid degeneration and small spindled and bipolar cells. Scant chronic inflammation was observed in most cases. GLUT1 immunostaining showed membranous patterns in all cases, with some cytoplasmic expression, particularly in stellate cells within the myxoid matrix. EMA staining exhibited focal membranous expression in 12 cases (85.71%) and was negative in two cases (14.29%). These findings highlight the importance of caution when evaluating core biopsies of soft tissue lesions with bland cystic and fibromyxoid histology. The morphological and immunohistochemical similarities between ganglion cysts and perineuriomas may pose a diagnostic challenge and risk of misinterpretation. Awareness of these overlaps is crucial to avoid potential pitfalls in diagnosis.